China's consumer prices fell slightly in May, while the annual decline in factory-gate prices deepened, official data showed on Monday.

The country's consumer price index, the main gauge of inflation, fell by 0.1 percent year-on-year in May, the same as in the previous month, according to the National Bureau of Statistics. But the core CPI, which excludes volatile food and energy prices and is deemed a better gauge of the supply-demand relationship, increased 0.6 percent year-on-year in May, up from a 0.5 percent rise in April.

Month-on-month, the CPI dipped 0.2 percent in May, following a 0.1 percent growth in April.

Dong Lijuan, an NBS statistician, attributed the CPI fall to the declining energy prices, adding that the factory-gate prices dropped mainly due to imported factors driving down prices of certain industries at home as well as the high comparison base in the previous year.

China's producer price index, which gauges factory-gate prices, dropped by 3.3 percent year-on-year in May, widening from a 2.7 percent fall in April, the NBS said.

On a month-on-month basis, the PPI dropped 0.4 percent in May, just as it did in April, according to the NBS.